Generally it is difficult for a molding machine which produces a plurality of products successively in a short time to measure an amount of powder material before the powder material is molded into a product in spite the products such as tablets are required to have a uniform weight. For a molding machine having an arrangement in which a punch is inserted into a die by a predetermined depth to compress powder material into a product a ratio of the weight of the product to the compressive pressure applied to the product is approximately one to one. In view of the above, compressive pressure acting on the powder material is detected and the amount of the powder material to be filled into the die is automatically controlled so that the detected compressive pressure becomes identical to a reference value of pressure which has previously been calculated in correspond with a target amount of the powder material. In accordance with a method which controls weight of a product indirectly, however, the weight of the product might fluctuate because a punch or a die expands or shrinks due to heat or a flow of the powder material fluctuates even if the compressive pressure is controlled to be identical to the reference value of pressure. Then conventionally the amount of the powder material to be filled into the die is adjusted so that the weight of the product which has been periodically sampled becomes identical to a reference value of weight and a reference value of pressure is calibrated based on compressive pressure measured after the amount of the powder material is adjusted.
Recent demand requires that thickness of products be within a certain range in order to make a process of packing the products smooth. In this case, position of a punch is controlled to make the thickness of a product identical to a reference value of thickness and the reference value of pressure is calibrated based on the compressive pressure when the thickness of the product is within the range.
However, weight and thickness are interconnected. Then if either one of them is controlled, the other would also be affected. As a result, it has conventionally been considered to be difficult to control both weight and thickness together and both of the weight and thickness can not automatically be controlled at once. Therefore, a skilled person adjusts the weight and thickness together manually, which prevents the manufacturing process from being automated. This is one of the factors which prevents productivity from being improved.